The threat of bioterrorism has reintroduced smallpox as a potential threat to public health and thereby established a need for novel treatments or prophylactic measures. The smallpox vaccine used during the worldwide vaccination program is associated with rare but serious adverse reactions, some fatal, thereby preventing mass vaccination. This application describes the pre-clinical development of a recombinant human polyclonal smallpox antibody to be used as a prophylactic or therapeutic agent against smallpox, and related orthopoxviruses. A specific and potent anti-orthopoxvirus polyclonal antibody will, enable countermeasure against smallpox, substitute the blood-derived vaccinia immunoglubulin (VIG), providing a significantly improved safety profile and product supply, decreased injection volumes, and easier route of injection, including the development of self-manageable injection devices for health care personnel and soldiers. This recombinant polyclonal antibody product will mirror the diversity, affinity and specificity of the natural human immune response. Because the polyclonal antibody is directed against multiple epitopes and proteins, the antibody is expected to be highly potent. The overall goal of the present project is to enable the filing of an IND. A polyclonal master cell line will be generated under GMP and validated with respect to genetic stability and sterility. The cell line will be used during development of a production process and scale-up. A downstream process for antibody purification, formulation, and fill-finish will be established. Processes and procedures already established in more advanced projects at Symphogen for production of therapeutic polyclonal antibodies can be adapted. The biological activity of the polyclonal antibody will be tested in the vaccinia lesion tail mouse model and a lethal mouse model. If the initial models show efficacy, the antiviral activity will also be assayed against monkeypox virus in a replication model in parallel with studies of binding to variola virus proteins. Combined, the data may provide evidence that the polyclonal antibody exerts both therapeutic and prophylactic activity against orthopoxviruses. The collected results from the proof of concept studies and production and purification processes will enable the filling of an IND.